Measuring and Reporting Electrical Conductivity in Metal–Organic Frameworks: Cd

Electrically conductive metal–organic frameworks (MOFs) are emerging as a subclass of porous materials that can have a transformative effect on electronic and renewable energy devices. Systematic advances in these materials depend critically on the accurate and reproducible characterization of their electrical properties. This is made difficult by the numerous techniques available for electrical measurements and the dependence of metrics on device architecture and numerous external variables. These challenges, common to all types of electronic materials and devices, are especially acute for porous materials, whose high surface area make them even more susceptible to interactions with contaminants in the environment. Here, we use the anisotropic semiconducting framework Cd₂(TTFTB) (TTFTB⁴⁻ = tetrathiafulvalene tetrabenzoate) to benchmark several common methods available for measuring electrical properties in MOFs. We show that factors such as temperature, chemical environment (atmosphere), and illumination conditions affect the quality of the data obtained from these techniques. Consistent results emerge only when these factors are strictly controlled and the morphology and anisotropy of the Cd2(TTFTB) single-crystal devices are taken into account. Most importantly, we show that depending on the technique, device construction, and/or the environment, a variance of 1 or even 2 orders of magnitude is not uncommon for even just one material if external factors are not controlled consistently. Differences in conductivity values of even 2 orders of magnitude should therefore be interpreted with caution, especially between different research groups comparing different compounds. These results allow us to propose a reliable protocol for collecting and reporting electrical properties of MOFs, which should help improve the consistency and comparability of reported electrical properties for this important new class of crystalline porous conductors.United States. Department of Energy. Office of Basic Energy Sciences (Award DE-SC0006937)National Science Foundation (U.S.) (Award 1122374

Electrochemical oxygen reduction catalysed by Ni3(hexaiminotriphenylene)2

Control over the architectural and electronic properties of heterogeneous catalysts poses a major obstacle in the targeted design of active and stable non-platinum group metal electrocatalysts for the oxygen reduction reaction. Here we introduce Ni[SUBSCRIPT 3](HITP)[SUBSCRIPT 2] (HITP=2, 3, 6, 7, 10, 11-hexaiminotriphenylene) as an intrinsically conductive metal-organic framework which functions as a well-defined, tunable oxygen reduction electrocatalyst in alkaline solution. Ni[SUBSCRIPT 3](HITP)[SUBSCRIPT 2] exhibits oxygen reduction activity competitive with the most active non-platinum group metal electrocatalysts and stability during extended polarization. The square planar Ni-N[SUBSCRIPT 4] sites are structurally reminiscent of the highly active and widely studied non-platinum group metal electrocatalysts containing M-N[SUBSCRIPT 4] units. Ni[SUBSCRIPT 3](HITP)[SUBSCRIPT 2] and analogues thereof combine the high crystallinity of metal-organic frameworks, the physical durability and electrical conductivity of graphitic materials, and the diverse yet well-controlled synthetic accessibility of molecular species. Such properties may enable the targeted synthesis and systematic optimization of oxygen reduction electrocatalysts as components of fuel cells and electrolysers for renewable energy applications.United States. Department of Energy. Office of Basic Energy Sciences (Award DESC0006937

High Electrical Conductivity in Ni 3 (2,3,6,7,10,11-hexaiminotriphenylene) 2 , a Semiconducting Metal–Organic Graphene Analogue

Reaction of 2,3,6,7,10,11-hexaaminotriphenylene with Ni2+ in aqueous NH3 solution under aerobic conditions produces Ni3(HITP)2 (HITP = 2,3,6,7,10,11-hexaiminotriphenylene), a new two-dimensional metalorganic framework (MOF). The new material can be isolated as a highly conductive black powder or dark blue-violet films. Two-probe and van der Pauw electrical measurements reveal bulk (pellet) and surface (film) conductivity values of 2 Scm -1 and 40 Scm -1, respectively, both records for MOFs and among the best for any coordination polymer.Chemistry and Chemical Biolog

Highly Coplanar Very Long Oligo(alkylfuran)s: A Conjugated System with Specific Head-To-Head Defect

Well-defined monodisperse conjugated oligomers, which have planar backbones and are free from the disturbance of substituents, attract broad interest. Herein, we report a series of symmetrical, isomerically pure oligofurans, namely, the 16-mer <b>16F-6C</b>_<b>6</b> together with the related <b><i>n</i>F-</b><b>2</b><b>C</b>_<b>6</b> (<i>n</i> = 4, 6, 8). Through computational studies and detailed spectroscopic and X-ray characterization, for the first time, we show that the planarity of the furan backbone is almost unaffected by the head-to-head defect which is known to cause considerable twists in its oligo- or poly­thiophene analogues. We present that the properties of these rigid oligo­(alkyl­furan)­s are strongly influenced by the conjugation length. As the longest monodisperse α-oligofuran synthesized to date, <b>16F-6C</b>_<b>6</b> was observed to be stable and highly fluorescent. Experimental and computational studies of the redox states of these oligo­(alkyl­furan)­s reveal that <b>16F-6C</b>_<b>6</b> has singlet biradical (polaron-pair) character in the doubly oxidized ground state: the open-shell singlet (⟨<i>S</i>₂⟩ = 0.989) is 3.8 kcal/mol more stable than the closed-shell dication

Discovery of blue singlet exciton fission molecules via a high-throughput virtual screening and experimental approach

Singlet exciton fission is a mechanism that could potentially enable solar cells to surpass the Shockley-Queisser efficiency limit by converting single high-energy photons into two lower-energy triplet excitons with minimal thermalization loss. The ability to make use of singlet exciton fission to enhance solar cell efficiencies has been limited, however, by the sparsity of singlet fission materials with triplet energies above the bandgaps of common semiconductors such as Si and GaAs. Here, we employ a high-throughput virtual screening procedure to discover new organic singlet exciton fission candidate materials with high-energy (>1.4 eV) triplet excitons. After exploring a search space of 4482 molecules and screening them using time-dependent density functional theory, we identify 88 novel singlet exciton fission candidate materials based on anthracene derivatives. Subsequent purification and characterization of several of these candidates yield two new singlet exciton fission materials: 9,10-dicyanoanthracene (DCA) and 9,10-dichlorooctafluoroanthracene (DCOFA), with triplet energies of 1.54 eV and 1.51 eV, respectively. These materials are readily available and low-cost, making them interesting candidates for exothermic singlet exciton fission sensitization of solar cells. However, formation of triplet excitons in DCA and DCOFA is found to occur via hot singlet exciton fission with excitation energies above ∼3.64 eV, and prominent excimer formation in the solid state will need to be overcome in order to make DCA and DCOFA viable candidates for use in a practical device.U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (grant no. DE-SC0001088

Importance of Unpaired Electrons in Organic Electronics

The first observation that PBBTPD, a low bandgap, ambipolar conjugated donor-acceptor (DA) polymer based on benzobisthiadiazole (BBT), possesses an open-shell singlet ground state as well as a thermally accessible triplet state is described. Similarly, interesting electronic behavior in semiconducting organic DA oligomers based on BBT is also observed. Theoretical predictions have suggested that such behavior is due to the biradicaloid character of BBT and we provide experimental evidence indicating that these predictions are correct. Furthermore, the open shell character strengthens as the conjugation length increases, as observed in the BBT-based polymer, PBBTPD. We show that this biradicaloid structure is observed in each BBT moiety along the chain and that therefore PBBTPD is in fact a polyradicaloid. This observation will most likely aid in the development of better n-type polymeric acceptors for organic semiconductor applications. (c) 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015, 53, 287-29

High Electrical Conductivity in Ni₃(2,3,6,7,10,11-hexaiminotriphenylene)₂, a Semiconducting Metal–Organic Graphene Analogue

Reaction of 2,3,6,7,10,11-hexa­amino­tri­phenyl­ene with Ni²⁺ in aqueous NH₃ solution under aerobic conditions produces Ni₃­(HITP)₂ (HITP = 2,3,6,7,10,11-hexa­imino­tri­phenyl­ene), a new two-dimensional metal–organic framework (MOF). The new material can be isolated as a highly conductive black powder or dark blue-violet films. Two-probe and van der Pauw electrical measurements reveal bulk (pellet) and surface (film) conductivity values of 2 and 40 S·cm^–1, respectively, both records for MOFs and among the best for any coordination polymer

A Microporous and Naturally Nanostructured Thermoelectric Metal-Organic Framework with Ultralow Thermal Conductivity

Microporous metal-organic frameworks (MOFs) offer attributes that make them potentially compelling choices for thermoelectric applications because they combine organic character with long-range order and intrinsically low thermal conductivity. So far, thermoelectricity in this class of materials has required infiltration with external molecules to render the framework electrically conductive. Here, we present thermoelectric studies on an n-type naturally nanostructured microporous MOF, Ni3(2,3,6,7,10,11-hexaiminotriphenylene)2, whose pressed pellets exhibit high electrical conductivity and low thermal conductivity. The results here show that by combining the structural rigidity and high crystallinity of inorganic materials, the solution-based synthesis of organic materials, and the unique pore-based tunability and low thermal conductivity, MOFs represent an intriguing new class of thermoelectric materials. Keywords: metal-organic framework; thermoelectrics; microporosity; nanostructuring; thermal insulator; electrical conductorUnited States. Department of Energy. Office of Basic Energy Sciences (Award DE-SC0001088

High Electrical Conductivity in Ni₃(2,3,6,7,10,11-hexaiminotriphenylene)₂, a Semiconducting Metal–Organic Graphene Analogue

Reaction of 2,3,6,7,10,11-hexa­amino­tri­phenyl­ene with Ni²⁺ in aqueous NH₃ solution under aerobic conditions produces Ni₃­(HITP)₂ (HITP = 2,3,6,7,10,11-hexa­imino­tri­phenyl­ene), a new two-dimensional metal–organic framework (MOF). The new material can be isolated as a highly conductive black powder or dark blue-violet films. Two-probe and van der Pauw electrical measurements reveal bulk (pellet) and surface (film) conductivity values of 2 and 40 S·cm^–1, respectively, both records for MOFs and among the best for any coordination polymer